| The performance of switching power supplies affects the stability of electronic equipment,and the level of inrush current suppression is a key factor in determining the stability of switching power supplies and their electronic equipment.The inrush current is the spike current that is much larger than the steady-state current generated by the circuit due to the charging of the input capacitor at the moment when the input power is connected to the circuit or in case of abnormal circuit conditions.The traditional inrush suppression scheme has limited suppression capability and inconsistent suppression capability when repeatedly powered on,and the suppression is still involved in the working process of the switching power supply at the end,which will have a negative impact on the working state and conversion efficiency of the switching power supply.In response to the above problems,this paper mainly develops the following work.(1)The design of the flyback transformer is completed based on the flyback topology for a low-power DC-DC converter.According to the requirements of the DC-DC converter,Power Stage Designer Tool design software is applied to calculate the turns ratio n,duty cycle D,and initial stage current variation_ΔI_Pand_ΔI_S more completely,and the core structure,wire diameter,and air gap size are determined according to the core saturation condition.The combination of both theoretical equation derivation and software verification makes the transformer design more accurate.(2)A PWM-type surge suppression circuit and its digital control strategy are proposed.Using the step-down function of the synchronous BUCK converter and the flexibility of the PWM digital control strategy,the rate of voltage rise across the input capacitor of the power supply circuit is slowed down so that the charging current of the input capacitor becomes smaller and the function of inrush suppression is achieved.At the same time,the use of a bypass switch at the end of the surge suppression in time to bypass the surge suppressor off,solving the impact of the surge suppressor on the operating state of the switching power supply and conversion efficiency.Compared with the traditional use of passive components to suppress inrush current program,the proposed PWM-type inrush suppression circuit has the advantage of good suppression effect,not affected by the ambient temperature;the use of digital chips to achieve control,through the microcontroller output four signals to control the entire system,with adjustable power-up rate,repeated power-up consistent advantage.simulation results of Simulink show that the proposed inrush Suppressor compared to the non-use of inrush suppressor its inrush current is reduced by 4.2 times,compared to the series inductor its inrush current is reduced by 2.7 times.(3)The designed PWM surge suppression circuit is actually prepared and tested experimentally.The test results show that compared with the traditional switching power supply circuit,the inrush current of the new circuit is reduced by 6 times.And under different input voltage,operating temperature and repeated power-on frequency,the new circuit can maintain a good surge current suppression effect.The inrush current can be suppressed under the test conditions of the input voltage range of 3.5-5.5V,and the inrush current can be suppressed within 4 times of the stable value of the input current when the bypass switch is turned on;at-10℃,25℃,60℃,the surge suppressor can work normally and maintain consistent surge suppression capability;under the repeated power-on test conditions with a repetition frequency of 1KHz,the surge current can still be suppressed. |
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